1. Field of the Invention
The present invention relates to a molten metal casting apparatus and, more particularly, a casting apparatus including a gas driven molten metal injector.
2. Description of the Prior Art
Numerous furnace-ladling devices are known in the art for delivering molten metal from a molten metal container or vessel to a desired point of use, such as a die casting machine. Such devices often include a crucible body that includes a molten metal inlet tube and a molten metal delivery tube for delivering molten metal to a point above the crucible. The molten metal inlet and delivery tubes generally define vertically extending passages through which molten metal from the container or vessel is able to pass through the crucible. The molten metal inlet tube extends upward into the crucible and defines an opening above the operating level of molten metal contained in the crucible. A gas inlet tube provides a third passage into the crucible and through which the crucible may be pressurized to force the molten metal into the delivery tube.
U.S. Pat. No. 3,471,057 to Solheim and U.S. Pat. No. 3,876,191 to Lauersdorf are examples of such furnace-ladling devices known in the art. The crucibles for these devices may be partially or completely submerged in the molten metal in the container or vessel. A known disadvantage with such devices is that the molten metal inlet tube extending upward into the crucible, in operation, allows molten metal to spill over or xe2x80x9cfree fallxe2x80x9d over the top of the tube to refill the crucible. Such a spilling effect often causes metal oxides to form within the crucible and reduces the overall quality of the cast product ultimately made from the molten metal contained in the crucible. The pressure applied to the metal injected is limited by the height of the molten metal inlet tube used to refill the crucible.
U.S. Pat. No. 4,216,886 to Puschalovsky et al. (hereinafter xe2x80x9cthe Puschalovsky patentxe2x80x9d) improves upon the arrangement disclosed by the Solheim and Lauersdorf patents by providing a submergible crucible having an inlet opening in the top wall of the crucible and a closing device for selectively closing the inlet opening. However, because the inlet opening is located in the top wall of the crucible, the crucible molten metal enters through the inlet opening during refilling operations and xe2x80x9cfree fallsxe2x80x9d into the interior of the crucible. Accordingly, the same molten metal quality issues that exist with the arrangements disclosed by the Solheim and Lauersdorf patents are also present in the arrangement disclosed by the Puschalovsky patent.
U.S. Pat. No. 5,846,445 to Umino discloses an apparatus for transferring molten metal that includes a molten metal chamber positioned within a metal furnace. The molten metal chamber is connected to a bottom wall of the furnace. A fluid feed pipe communicates with the chamber through a sidewall of the chamber. The fluid feed pipe operates as both a molten metal inlet conduit and a molten metal discharge conduit for the chamber. A gas inlet/outlet pipe communicates with the chamber through a top wall of the chamber. The arrangement disclosed by the Umino patent is substantially similar to the arrangements disclosed by the Solheim and Lauersdorf patents, but includes a single molten metal inlet and discharge conduit and the chamber is physically attached to the bottom of the furnace. The arrangement disclosed by the Umino patent overcomes the molten metal xe2x80x9cfree fallxe2x80x9d problems present in the arrangements disclosed by the Solheim and Lauersdorf patents, but due to the position of the chamber and the vertical length of the discharge conduit from the chamber, the arrangement disclosed by the Umino patent is very limited in available operating pressures and there is no means provided to prevent backflow of molten metal into the furnace from the chamber. The flow of molten metal out of the furnace cannot be accurately controlled and the pressure is extremely limited and difficult to control.
U.S. Pat. No. 5,913,358 to Chadwick discloses a casting apparatus that includes a holding furnace for holding a reservoir of molten metal and a smaller pumping furnace in fluid communication with the holding furnace through a non-return, ball check valve. The pumping furnace is integrally formed with the holding furnace. The ball check valve prevents the flow of molten metal from the pumping furnace to the holding furnace during pressurization of the pumping furnace, but allows the flow of molten metal from the holding furnace to the pumping furnace after pressurization.
The holding furnace/pumping furnace arrangement disclosed by the Chadwick patent has several drawbacks. First, the ball check valve providing the connection between the holding furnace and the pumping furnace is a passive device that provides little ability to control the inflow of molten metal to the pumping furnace. In addition, the use of ball check valves in such molten metal transfer arrangements is known to have practical disadvantages. In particular, ball check valves require clean molten metal flows to operate effectively. The introduction of metal oxide particulates in the molten metal flows will cause the roller ball of the ball check valve to stick or prevent its full closing position from being obtained and this will require that the furnace be drained and the ball check valve cleaned. Further, the integrally formed holding furnace/pumping furnace arrangement disclosed by the Chadwick patent provides little flexibility in dosing molten metal to downstream processes such as a die casting machine. The position of the pumping furnace is fixed with respect to the holding furnace, which limits the locations from which molten metal may be dosed from the holding furnace/pumping furnace arrangement.
In view of the foregoing, it is an object of the present invention to provide a casting arrangement that includes a gas driven molten metal injector that provides the ability to control the inflow and filling of molten metal into the injector. In addition, it is an object of the present invention to provide a casting apparatus that includes a plurality of gas driven molten metal injectors that may be independently positioned and operated in a molten metal holding vessel. It is a further object of the present invention to provide a gas driven molten metal injector that improves metal quality delivery to downstream processes. This invention provides for accurate control of injected molten metal flow rate and subsequent holding pressure applied to metal held in a mold cavity of a die casting machine.
The above objects are accomplished with a casting apparatus made in accordance with the present invention. The casting apparatus includes a holding vessel for containing a supply of molten metal. A casting mold is located above the holding vessel and defines a casting cavity. A molten metal injector extends into the holding vessel and is at least partially immersed in molten metal when the holding vessel contains the supply of molten metal. The molten metal injector includes an injector body that defines an inlet opening for receiving molten metal into the injector body from the supply of molten metal contained in the holding vessel. A gas pressurization source is in fluid communication with the injector body for cyclically pressurizing the injector body and inducing molten metal to flow from the injector to the casting cavity of the casting mold, and for exhausting to atmospheric pressure to permit filling of the injector body with molten metal. An inlet valve is located in the inlet opening in the injector body for filling molten metal into the injector body. The inlet valve is configured to prevent outflow of molten metal from the injector body during pressurization of the injector body and permit inflow of molten metal (i.e., filling/refilling) into the injector body after pressurization. The inlet valve has an inlet valve actuator located above the surface of the supply of molten metal and is operatively connected to the inlet valve for operating the inlet valve between an open position allowing for the filling of the injector body with molten metal and a closed position allowing for the pressurization of the injector body. The gas pressurization source may be operable to pressurize the injector body when the inlet valve is in the closed position and to exhaust to atmospheric pressure when the inlet valve is open.
The injector body may be defined by a top wall, sidewalls, and a bottom wall. The gas pressurization source may be in fluid communication with the injector body through the top wall of the injector body. The inlet opening may be provided as an inlet conduit extending from one of the sidewalls of the injector body. The inlet valve may be located in the inlet conduit.
The injector body may include a fill tube extending into the injector body and in fluid communication with the casting cavity. The fill tube may be integrally formed with the injector body. A molten metal filter may cover the inlet opening for filtering the molten metal entering the injector body through the inlet opening. The fill tube may define an opening within the injector body. A second molten metal filter may cover the opening to the fill tube. The injector body and the inlet valve may be made of graphite, ceramic material, or a mixture of graphite and ceramic material.
The present invention is also directed to a gas driven molten metal injector for use with a holding vessel containing a supply of molten metal. The molten metal injector includes an injector body defining an inlet opening for receiving molten metal into the injector body from the supply of molten metal when the injector body is at least partially immersed in the supply of molten metal. A fill tube extends into the injector body for dosing molten metal from the injector body to a downstream process. A gas pressurization source is in fluid communication with the injector body for cyclically pressurizing the injector body and inducing molten metal to flow into the fill tube, and for exhausting to atmospheric pressure to permit filling of the injector body with molten metal. An inlet valve is located in the inlet opening in the injector body for filling molten metal into the injector body. The inlet valve is configured to prevent outflow of molten metal from the injector body during pressurization of the injector body and permit inflow of molten metal into the injector body after pressurization. An inlet valve actuator is operatively connected to the inlet valve for operating the inlet valve between an open position allowing for the filling of the injector body with molten metal and a closed position allowing for the pressurization of the injector body. The gas pressurization source may be operable to pressurize the injector body when the inlet valve is in the closed position and to exhaust to atmospheric pressure when the inlet valve is open.
Furthermore, the present invention is a method of casting a metal component that may include the steps of: providing a holding vessel containing a supply of molten metal; locating a casting mold above the holding vessel with the casting mold having a casting cavity; positioning a molten metal injector in the holding vessel such that the molten metal injector is at least partially immersed in the supply of molten metal, with the molten metal injector in fluid communication with the casting cavity of the casting mold, with the molten metal injector having an injector body defining an inlet opening for receiving molten metal into the injector body from the supply of molten metal contained in the holding vessel, and with the molten metal injector having an inlet valve located in the inlet opening in the injector body and having an inlet valve actuator connected to the inlet valve for operating the inlet valve between an open position and a closed position; placing a gas pressurization source in fluid communication with the injector body for cyclically pressurizing the injector body and inducing molten metal to flow from the molten metal injector to the casting cavity of the casting mold and for exhausting to atmospheric pressure to permit filling of the injector body with molten metal; operating the inlet valve to the open position to allow filling (i.e., refilling) of molten metal into the injector body through the inlet opening; operating the inlet valve to the closed position after the injector body is at least partially filled with molten metal; and pressurizing the injector body with the gas pressurization source to induce molten metal to flow from the injector body to the casting cavity of the casting mold.
The method according to the present invention may include the steps of filtering the molten metal entering the injector body through the inlet opening and filtering the molten metal within the injector body before passing the molten metal to the casting cavity of the casting mold. The inlet valve actuator may be located above the surface of the supply of molten metal contained in the holding vessel, and the method may further include the step of operating the inlet valve between the open and closed positions from above the surface of the molten metal with the inlet valve actuator. The injector body may be provided with an integrally formed and vertically extending fill tube in fluid communication with the casting cavity of the casting mold. Further, the method according to the present invention may include the step of depressurizing the injector body after a set duration of time to allow the molten metal received in the casting cavity of the casting mold to substantially solidify.
The method may also include the steps of positioning a plurality of the molten metal injectors in the holding vessel such that each of the molten metal injectors is at least partially immersed in the supply of molten metal and independently operating the inlet valve and gas pressurization source for each of the molten metal injectors. The step of independently operating the inlet valve and gas pressurization source for each of the molten metal injectors may be performed by a programmable logic controller or a programmable computer. The inlet valve and gas pressurization source for each of the molten metal injectors may be operated such that each of the plurality of molten metal injectors doses molten metal to the casting cavity of the casting mold at different times and at different rates. The injector body for each of the molten metal injectors may be depressurized substantially simultaneously after a set duration of time has elapsed to allow the molten metal in the casting cavity to substantially solidify. The inlet valve and gas pressurization source for each of the molten metal injectors may be further operated such that at least two of the plurality of molten metal injectors dose molten metal to the casting cavity of the casting mold at substantially the same time and at substantially the same rate.
Further details and advantages of the present invention will become apparent from the following detailed description read in connection with the drawings.